To refine and expand a conceptual framework for systematic classification of presently unorganized evidence relating to effects of hormones on behavior. The schema is based on a 3-dimensional matrix which facilitates integration of evidence pertaining to: (1) effects of hormones on different physiological target systems from single cells, to tissues and organs, to the complete organism; (2) effects of hormones on behavior of the total organism at different stages of ontogeny from fetal, to infancy and prepuberty, to adolescence, to maturity; (3) effects of hormones on different psychological states or processes such as learning, memory, motivation, etc. Preliminary tests indicate that the proposed approach may help to solve 3 fundamental problems currently facing behavioral endocrinology. (1) It provides a logically organized framework within which a great deal of currently unorganized empirical evidence can be systematically classified, so that theoretically useful generalizations begin to emerge. (2) It throws in sharp relief important areas in which research is urgently needed; raises questions for which no relevant data are available, but which must be resolved in the interest of building testable theories. (3) It compels recognition of fundamental similarities and differences between species. One consequence is that the schema forces attention to the theoretical and practical values of increased research on human beings. The three-dimensional matrix clearly shows that information regarding hormones and human behavior is essential to provide the basis for comprehensive theory. At the same time it clarifies issues regarding the relevance of animal research to problems of mental health. Some research on animals currently used as a model for problems in human sexuality is totally inappropriate and dangerously misleading. Some is genuinely relevant and already has been successively extended in treatment of human health problems. Most important of all, the proposed theoretical orientation brings to light new areas in which future research on both animals and human beings could yield evidence capable of increasing our understanding and perhaps treatment of specific problems in mental health.